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cannonfield.cpp Example File
^{tutorial/t12/cannonfield.cpp}

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    **
    ** This file is part of the documentation of the Qt Toolkit.
    **
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    ** and appearing in the file LICENSE.GPL included in the packaging of
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    #include <QDateTime>
    #include <QPaintEvent>
    #include <QPainter>
    #include <QTimer>

    #include <math.h>
    #include <stdlib.h>

    #include "cannonfield.h"

    CannonField::CannonField(QWidget *parent)
        : QWidget(parent)
    {
        currentAngle = 45;
        currentForce = 0;
        timerCount = 0;
        autoShootTimer = new QTimer(this);
        connect(autoShootTimer, SIGNAL(timeout()), this, SLOT(moveShot()));
        shootAngle = 0;
        shootForce = 0;
        target = QPoint(0, 0);
        setPalette(QPalette(QColor(250, 250, 200)));
        setAutoFillBackground(true);
        newTarget();
    }

    void CannonField::setAngle(int angle)
    {
        if (angle < 5)
            angle = 5;
        if (angle > 70)
            angle = 70;
        if (currentAngle == angle)
            return;
        currentAngle = angle;
        update(cannonRect());
        emit angleChanged(currentAngle);
    }

    void CannonField::setForce(int force)
    {
        if (force < 0)
            force = 0;
        if (currentForce == force)
            return;
        currentForce = force;
        emit forceChanged(currentForce);
    }

    void CannonField::shoot()
    {
        if (autoShootTimer->isActive())
            return;
        timerCount = 0;
        shootAngle = currentAngle;
        shootForce = currentForce;
        autoShootTimer->start(5);
    }

    void CannonField::newTarget()
    {
        static bool firstTime = true;

        if (firstTime) {
            firstTime = false;
            QTime midnight(0, 0, 0);
            srand(midnight.secsTo(QTime::currentTime()));
        }
        target = QPoint(200 + rand() % 190, 10 + rand() % 255);
        update();
    }

    void CannonField::moveShot()
    {
        QRegion region = shotRect();
        ++timerCount;

        QRect shotR = shotRect();

        if (shotR.intersects(targetRect())) {
            autoShootTimer->stop();
            emit hit();
        } else if (shotR.x() > width() || shotR.y() > height()) {
            autoShootTimer->stop();
            emit missed();
        } else {
            region = region.unite(shotR);
        }
        update(region);
    }

    void CannonField::paintEvent(QPaintEvent * /* event */)
    {
        QPainter painter(this);

        paintCannon(painter);
        if (autoShootTimer->isActive())
            paintShot(painter);
        paintTarget(painter);
    }

    void CannonField::paintShot(QPainter &painter)
    {
        painter.setPen(Qt::NoPen);
        painter.setBrush(Qt::black);
        painter.drawRect(shotRect());
    }

    void CannonField::paintTarget(QPainter &painter)
    {
        painter.setPen(Qt::black);
        painter.setBrush(Qt::red);
        painter.drawRect(targetRect());
    }

    const QRect barrelRect(30, -5, 20, 10);

    void CannonField::paintCannon(QPainter &painter)
    {
        painter.setPen(Qt::NoPen);
        painter.setBrush(Qt::blue);

        painter.save();
        painter.translate(0, height());
        painter.drawPie(QRect(-35, -35, 70, 70), 0, 90 * 16);
        painter.rotate(-currentAngle);
        painter.drawRect(barrelRect);
        painter.restore();
    }

    QRect CannonField::cannonRect() const
    {
        QRect result(0, 0, 50, 50);
        result.moveBottomLeft(rect().bottomLeft());
        return result;
    }

    QRect CannonField::shotRect() const
    {
        const double gravity = 4;

        double time = timerCount / 20.0;
        double velocity = shootForce;
        double radians = shootAngle * 3.14159265 / 180;

        double velx = velocity * cos(radians);
        double vely = velocity * sin(radians);
        double x0 = (barrelRect.right() + 5) * cos(radians);
        double y0 = (barrelRect.right() + 5) * sin(radians);
        double x = x0 + velx * time;
        double y = y0 + vely * time - 0.5 * gravity * time * time;

        QRect result(0, 0, 6, 6);
        result.moveCenter(QPoint(qRound(x), height() - 1 - qRound(y)));
        return result;
    }

    QRect CannonField::targetRect() const
    {
        QRect result(0, 0, 20, 10);
        result.moveCenter(QPoint(target.x(), height() - 1 - target.y()));
        return result;
    }